Gene transfer therapy offers the potential for treatment of a variety of diseases. Naked plasmid DNA has been successfully used for both gene therapy and vaccine development. The mechanism mediating the binding and internalization of plasmid DNA by cells leading to gene expression remains undefined, Based on our studies of cell-surface DNA binding we hypothesize that a specific cell-surface DNA receptor is responsible for the binding and internalization of plasmid DNA. The specific aims of this proposal are to i) establish whether the binding, internalization, and subsequent expression of plasmid DNA is consistent with a receptor- mediated process, and ii) determine whether a candidate DNA receptor gene which we have cloned and sequenced codes for the DNA receptor protein. The molecular characterization of a receptor-mediated process for the binding and internalization of plasmid DNA will permit studies to explore the regulation of receptor expression. We speculate that increasing the number of receptors on target cells will improve the efficiency of uptake of plasmid DNA resulting in an enhanced therapeutic effect. Moreover, the ability to selectively increase or decrease receptor numbers on cells will permit the development of strategies for the targeting of plasmid DNA to specific tissues. PROPOSED COMMERCIAL APPLICATION: The design of DNA ligands, either DNA vaccines or DNA for gene therapy, with enhanced affinity for the DNA receptor, would result in increased binding and internalization by cells as compared to current DNA plasmids. Increased uptake would be predicted to correlate with an enhanced therapeutic effect. Also, the ability to selectively increase or decrease the number of receptors on cells would allow for targeting of plasmid DNA to specific tissues.